This invention relates generally to silicon light modulators.
A silicon light modulator or SLM uses an electric field to modulate the orientation of a liquid crystal (LC) material. By the selective modulation of the liquid crystal material, an electronic display may be produced.
The orientation of the LC material affects the intensity of light going through the LC material. Therefore, by sandwiching the LC material between a reflective electrode and a transparent top plate, the optical properties of the LC material may be modulated.
In particular, by changing the voltage applied across the electrodes, the intensity of the light being reflected by the reflective electrode may be modulated, thereby changing its gray level value. When light is shined on the cell, the reflected light can produce an image on a screen. By changing the voltage level on the electrodes, the image can be altered.
Generally, a silicon light modulator includes a transparent conducting layer that acts as the top plate and a pixel electrode that acts as the reflective electrode. As the voltage on the pixel electrode changes, the reflected light intensity from the pixel area changes accordingly.
A transfer function, shown in FIG. 5, describes the relationship between the voltage applied and the resulting light brightness. As the voltage increases, the pixel brightness or gray scale generally increases too. A number of gray scale levels may be represented, such as 256 levels, by dividing the available voltage up accordingly.
However, typical liquid crystal material needs a relatively high voltage for modulation. Generally the upper level of top plate voltage, Vb, is between 3.3 and 10 volts.
The supply voltage of modern silicon chips is moving downwardly from 2.5 volts towards 1.3 volts and potentially lower thereafter. Therefore, leading edge integrated circuit chips may not have the sufficient voltage levels to modulate typical liquid crystal materials. This may adversely affect the ability to integrate displays into silicon chips.
Thus there is a need for better ways to use available voltage levels, such as voltage levels associated with leading edge integrated circuit chips, for modulating liquid crystal displays.